I should create for my nephew a website for solar cells and wind turbines. As I read about 2 years ago in a forum I should use for SEO-purposes a main domain and link from there to the two others and also interlink the secondary domains. Is this still true nowadays or should I use only one domain as a kind of portal. Also the question is if I use secondary domains, should I use them as subdomains, like www.solarcells.maindomain.xx or independent domains, like www.solarcells.xx?
It would be great if someone could help me.
Thanks in advance.